How to Change the Oil in a 1979 Kawasaki KX250

Shop parts for a 1979 Kawasaki KX250 Dirt Bike.

Changing the oil in your vintage 1979 Kawasaki KX250 is a fundamental maintenance procedure to keep the engine and transmission running smoothly. As a classic two-stroke dirt bike, the KX250 requires regular transmission oil changes, as there is no engine oil in a two-stroke; the fuel/oil mix lubricates the top end while the transmission uses a separate gear oil. Follow these step-by-step instructions for an effective, mess-free oil change that prolongs the life of your gearbox and clutch.

Tools and Supplies Needed

  • Socket set (including 12mm or 13mm for drain bolt, depending on your model)
  • Torque wrench
  • Drain pan
  • Funnel
  • Clean rags or paper towels
  • Transmission/gear oil (recommended: 80W or 80W–90 gear oil or a product like Maxima MTL 80W)
  • Ratio Rite measuring cup (to ensure precise oil quantity)
  • Gloves (optional, but recommended)

Step-by-step Instructions

  1. Warm Up the Engine:
    • Start the bike and let it idle for 2–3 minutes. This heats up the oil to help it flow out completely.
    • Turn off the engine before proceeding.
  2. Prepare for Draining:
    • Put the bike upright and place it on a stand.
    • Locate the transmission oil drain bolt.
      For the 1979 KX250, the drain plug is typically found underneath the right side of the engine case.
    • Set your drain pan directly under the drain bolt.
  3. Remove the Drain Bolt:
    • Use the appropriate socket to slowly loosen and remove the bolt. Be careful as the oil may be hot.
    • Allow old oil to drain completely – this may take several minutes.
    • Wipe any metal shavings off the drain bolt if it has a magnetized tip.
  4. Replace and Tighten Drain Bolt:
    • Once oil stops dripping, clean the drain area and reinstall the drain bolt by hand to avoid cross-threading.
    • Use your torque wrench to tighten the bolt to manufacturer spec. For older KX250s, a safe ballpark is 11–15 ft-lbs, but check your service manual.
      If unsure, err on the side of less torque to avoid stripping the case.
  5. Add New Transmission/Gear Oil:
    • Remove the oil filler cap located on the clutch cover.
    • Using your funnel and measuring cup, pour in the manufacturer-specified quantity of oil (typically 650ml/0.69 US quarts for vintage KX250s). Consult your owner's manual for the exact volume.
    • Be careful not to overfill. Use the sight glass or dipstick (if equipped) on the right engine case to check the level. The oil should sit in the center of the inspection window or at the proper line on the dipstick.
  6. Let the Oil Settle and Check Level:
    • Wait 1–2 minutes for the oil to settle, then double-check the level. Add a small amount if necessary, but do not overfill.
  7. Replace Filler Cap and Clean Up:
    • Replace the oil cap securely. Clean up any spilled oil, dispose of used oil responsibly.
    • Start the engine and let it idle for 1–2 minutes. Then turn it off and check the oil level one last time, making sure there are no leaks around the drain bolt or filler area.

1979 KX250 Model-Specific Call-Outs

  • Do NOT over-tighten the drain bolt on a vintage engine, as the case material is softer and more prone to stripping than modern bikes.
  • Gearbox oil type is critical: Use the correct non-friction-modified gear oil (such as 80W) designed for wet clutch systems; avoid automotive oils with additives unsuitable for dirt bike transmissions.
  • No oil filter to change — two-strokes like the 1979 KX250 use a simple gearbox oil system without an external or cartridge filter.
  • Inspect for leaks after the first ride, as older bikes may have brittle gaskets or worn seals.
  • Check the clutch feel after changing the oil; improper oil can lead to clutch slippage or engagement issues.

Additional Tips for 1979 Kawasaki KX250 Owners

  • Change gearbox oil after every 5–10 hours of riding, or after pounding harsh tracks, as dirt and water can easily contaminate older bikes with less effective seals.
  • If you notice milky or gray oil, it could mean water ingress — check gaskets and seals.
  • Always use quality oil from reputable brands to ensure optimal transmission and clutch life.
  • Keep good records: note the type and amount of oil used and the date of service for future reference.

Following these steps helps preserve the legendary performance and reliability of your vintage 1979 Kawasaki KX250 on every ride. For OEM and aftermarket parts, always trust MotoSport.com for the best in dirt bike service and support.

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Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.